This invention relates to a monolithic integrated circuit for a telephone circuit for centrally fed subscriber stations having a microphone amplifier and a receiving amplifier, wherein the conventionally used hybrid transformer is replaced by a resistance bridge and wherein the receiving and microphone amplifiers are constructed as monolithic integrated differential amplifiers.
Monolithic integrated circuit arrangements are known in the art. Further, integrated circuit subscriber station constructions are known which have the hybrid transformer replaced by a resistance bridge and wherein in one diagonal of the bridge a receiver is provided having an audio amplifier and in another diagonal of the bridge a microphone is provided but without an amplifier. Reference is made to the German Pat. Publication No. 1,762,058. Thus, in these prior art circuit arrangements there is no provision at the transmitting end for amplifying the message or voice signal.
Other conventional circuit arrangements are of discrete or hybrid design, having a resistance bridge instead of the hybrid transformer and wherein an audio amplifier is disposed in one bridge diagonal and a microphone amplifier is disposed in the other bridge diagonal. Reference is made to French Pat. No. 1,521,690, wherein, however, the decoupling of the amplifiers is achieved by means of component parts which cannot be used for an integrated circuit arrangement.
This invention has as an object the provision of a monolithic integrated circuit arrangement for a telephone circuit which can be connected to each subscriber line, while maintaining decoupling of the microphone and receiving amplifiers.